This invention relates to an improved vehicle compounded with abrasive grit for use in lapping operations and to a method for improving metal lapping operations. More particularly, this invention relates to an improved lapping composition consisting of an abrasive grit and a vehicle which comprises a hydrocarbon liquid and a gelling additive which has an enhanced ability to suspend abrasive grits, and to an improved lapping process.
Lapping is a low-speed, low-pressure abrading operation used in finishing metal parts to accomplish correction of minor imperfections in shape and/or refinement of the surface finish. Lapping is widely used, for example, in gear finishing to correct heat-treatment distortion errors, and for finishing flat surfaces of parts to achieve improved flatness and finish. Lapping is accomplished by rubbing the abrasive against the workpiece with a lap. Although in some operations the lap will have the abrasive bonded thereto, free abrasive lapping wherein the particulate abrasive is fed to the face of the lap is widely practiced. In free abrasive lapping operations, the particulate abrasive material is carried in a vehicle which suspends and carries the abrasive and lubricates or cushions the interface between the lap and the workpiece to minimize metal-to-metal contact. Oil-based vehicles are widely employed for these purposes, and may be such liquids as kerosene, diesel fuel, mineral seal oil, spindle oil and the like. For some purposes, heavy oils and greases are used, and commercial compositions employing mixtures of animal fats, vegetable and mineral oils are widely available.
In most lapping operations a mixture of the vehicle and the particulate abrasive or grit is continuously fed to the surface of the lap at a predetermined rate, collected in a sump area beneath the lap, and recirculated by pumping means. It will be apparent that uniform dispersion of the grit in the vehicle is desirable to accomplish a controlled, uniform feeding to the lap. In order to maintain a uniform dispersion, the reservoir containing the vehicle and grit mixture is normally agitated by stirring or similar means to prevent the grit from settling to the bottom. Similarly, where the grit and vehicle mixture is collected in a separate sump it is necessary that agitation and/or rapid removal of the mixture be accomplished in order to prevent settling and accumulation of grit in the sump area. While employing more viscous vehicles would tend to retard settling, highly viscous fluids are unsuited to most lapping operations and additionally are more difficult to mix and transport, requiring larger pumps and a more powerful stirring or mixing apparatus.
An improved vehicle composition having the ability which maintains the grit in suspension at the working viscosity either without agitation or with minimal stirring and which can be prepared to have any desired working viscosity within a wide range would clearly be a desirable advance in the art.